1. Technical Field
The present disclosure relates to a package which houses a semiconductor element, and particularly to a physical quantity sensor for use in attitude control, a navigation system, etc., for mobile objects such as aircrafts, vehicles, etc.
2. Description of the Related Art
Conventionally known such packages include packages used for physical quantity sensors such as a gyroscope. Conventional packages have a configuration as illustrated in FIG. 16 and FIG. 17 for suppressing cracking due to concentration of stress approximately at the center portion of an outer surface of a case.
FIG. 16 illustrates a cross-sectional side surface of a conventional package. FIG. 17 illustrates a lid of the conventional package in a top view.
As illustrated in FIG. 16 and FIG. 17, the conventional package is a physical quantity sensor, and includes integrated circuit (IC) 1 and case 2. In IC 1, a detection element (not illustrated) such as a piezoelectric vibrator is disposed. IC 1 processes an output signal from the detection element. Case 2 is made of glass ceramics, for example, and houses IC 1.
Case 2 includes power electrode 3, output electrode 4, and a ground (GND) electrode (not illustrated), on an outer bottom surface. Power electrode 3, output electrode 4, and the GND electrode (not illustrated) are electrically connected to IC 1 and the detection element (not illustrated) via wiring conductor 5 and lead 6. In addition, metallization layer 7 is disposed on an upper surface of case 2.
Metal frame 8 is disposed on metallization layer 7. Metal frame 8 is made of, for example, an alloy of Fe, Ni, and Co, and is brazed to metallization layer 7. Lid 9 is disposed on metal frame 8. Lid 9 is made of, for example, an alloy of Fe, Ni, and Co, and is joined to metal frame 8 by brazing, for example. As illustrated in FIG. 17, lid 9 has a shape of square parallelepiped in a top view.
Bent portion 10 is formed in lid 9. Bent portion 10 has a shape curved to protrude downward, and is formed in a more interior position on lid 9 than joint portion 11 between metal frame 8 and lid 9, and along joint portion 11 to extend over the whole circumference of lid 9.
The following describes, in particular, a method of attaching lid 9 to case 2 of the conventional package configured as described above.
First, Joule heat is generated by supplying current via metal frame 8 to lid 9 disposed in an opening of case 2, and a connecting portion of lid 9 made of the alloy of Fe, Ni, and Co is heated to the melting point of 1449 degrees Celsius to be melted. Next, lid 9 is pressed toward case 2 to connect case 2 and lid 9 with each other. At this time, the temperature of lid 9 as a whole increases to approximately 700 degrees Celsius on average.
Subsequently, lid 9 shrinks when the temperature of the package decreases to room temperature. At this time, there are instances where a crack appears in the outer surface of case 2 due to tensile stress applied to the outer surface of case 2 as a result of shrinking of lid 9.
For that reason, the conventional package has bent portion 10 in lid 9. In this manner, even if lid 9 shrinks, bent portion 10 bends to reduce the tensile stress applied to the outer surface of case 2, and thus it is possible to suppress cracking in the outer surface of case 2.
Bent portion 10, as described above, is formed in a more interior position on lid 9 than joint portion 11 between metal frame 8 and lid 9, and along joint portion 11 to extend over the whole circumference of lid 9. For this reason, in lid 9 having a square shape in a top view, it is possible to uniformly reduce the tensile stress that is generated in four sides of lid 9.
For example, Japanese Unexamined Patent Application Publication No. 2006-332599 is known as information on background art documents related to the disclosure of this application.
However, in the case where lid 9 of the above-described conventional package has a rectangular shape in a top view, when bent portion 10 is formed in a more interior position on lid 9 than joint portion 11 between case 2 (metal frame 8) and lid 9, and along joint portion 11 to extend over the whole circumference of lid 9, the tensile stress applied to short-side areas of lid 9 is significantly reduced due to bent portion 10 formed in the short-side areas of lid 9. As a result, von Mises stress that is represented by a scalar value increases. Accordingly, stress concentrates approximately at the center portions of longitudinal-side areas of the outer surface of case 2 which correspond to longitudinal-side areas of lid 9, posing a problem that it is difficult to suppress cracking in the outer surface of case 2.